Multiple channel electrocardiograph

ABSTRACT

The specific disclosure provides a multiple channel electrocardiograph wherein three body voltage measurements are simultaneously read-out on a moving chart. The electrocardiograph comprises means for automatically changing the body voltage measurements that are recorded on the chart, and means including a selectively operable circuit for automatically attentuating chest voltage measurements taken in vicinity of the heart.

United States Patent 1 Graetz MULTIPLE CHANNEL ELECTROCARDIOGRAPH [75]Inventor: Ernest F. J. Graetz, Derry, NH.

[73] Assignee: Parke, Davis & Company, Detroit,

Mich.

22 Filed: Mar. 4, 1974 21 Appl. No; 448,173

Related US. Application Data [63] Continuation of Ser. No. 281,074, Aug.16, 1972,

abandoned.

[52] US. Cl l28/2.06 G, 330/29, 330/86 [51] int. Cl A6lb 5/04 8 Field ofSearch 128/206 A, 2.06 B, 2.06 F, 128/206 G, 2.06 R, 2.1 R; 330/28, 29,30 D,

[56] References Cited UNITED STATES PATENTS 1l/1953 Miller 128/206 B10/1962 Daneman 128/206 B 9/1967 Kirkham 128/206 B 2/1968 Argy et all128/206 B 1 Mar. 4, 1975 Primary Examiner-William E. Kamm Attorney,Agent, or Firm-James F. Powers, Jr.; Albert H. Graddis [57] ABSTRACT Thespecific disclosure provides a multiple channel electrocardiographwherein three body voltage measurements are simultaneously read-out on amoving chart. The electrocardiograph comprises means for automaticallychanging the body voltage measurements that are recorded on the chart,and means including a selectively operable circuit for automaticallyattentuating chest voltage measurements taken in vi-.

cinity of the heart.

9 Claims, 12 Drawing Figures PATENTED CHANNEL 1 CHANNEL 2 CHANNEL 3SHEET 3 OF 9 78 a4 90 96 fl M00 GALV. STYLUS ,60 5 92 98 /04 //0 M00GALV. STYLUS g2 88 94 /00 /Q6 2 MOD GALV. STYLUS PATENTED 4i9-75 SHEET 5OF 9 .lllllll-IIIIIIlI-ll FATENTEUHAR 4175 3,868,948

sum 7 0f 9 IAl/R, AVL,AVF

I LEADS 1,2,3

MULTIPLE CHANNEL ELECTROCARDIOGRAPH This is a continuation ofapplication Ser. No. 281,074, filed Aug. 16, 1972, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to amulti-channel electrocardiograph. More particularly, the presentinvention relates to automatically changing the body voltagemeasurements printed out by an electrocardiograph, and to automaticallyreducing the amplitudes of the body voltage measurements taken in thevicinity of the heart.

An electrocardiograph is an instrument which records a heart cycleconsisting of atrial contraction, ventricular contraction and heartrest. The electrocardiograph typically prints out an electrocardiogramrepresentative of electrical potentials measured between various pointson the body surface during the heart cycle.

Multiple channel electrocardiographs are known in the art. For example,U.S. Pat. Nos. 2,627,267, 2,630,797 and 2,684,278 each discloseelectrocardiographs wherein three different electrical potential bodymeasurements are simultaneously processed and readout on a moving chart.An advantage of simultaneously printing out a plurality of measurementsis that a physician, cardiologist, or a disgnostician can obtain theinformation separately revealed by each of the plurality ofmeasurements, and can also consider the plurality of measurements in acorrelated manner at any particular instant of time along a common timecoordinate. This advantage not only minimizes the problem of correlatingsequentially generated cardiograms, but also provides a plurality ofcardiograms generated with assurance that the subjects heart conditionis identical for each one of the plurality of cardiograms.

Typically, a cardiogram records (1) a plurality of inter-extremitypotentials such as between the right arm and the left arm, (2) thepotential differences between extremities and averages of otherextremities such as between the right arm and the average of the leftarm and the left leg, and (3) the potential differences between each oneof a plurality of chest positions in the vicinity of the heart and anaverage of the right arm, the left arm and the left leg potentials.Since the chest potentials are in the vicinity of the heart, the chestsignals are significantly larger than the inter-extremity potentials.These high amplitude chest signals would tend to drive a recordingstylus off a chart paper unless the electrocardiograph includes acompensating circuit. U.S. Pat. No. 2,684,278 discloses a manuallyoperable means for reducing chest signals prior to their application toa recording stylus.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided an improvement in an electrocardiograph comprising aplurality of parrallel signal processing channels having means foramplifying signals, means for simultaneously applying a plurality ofsignals representative of different body electrical potentials includingpotentials in the vicinity of the heart to respective ones of thechannels, and means connected to the outputs of the channels forsimultaneously displaying a plurality of graphic representations of thebody electrical potentials.

The improvement in accordance with the present invention comprises meansfor automatically changing the applying means to sequentially applydifferent pluralities of body electrical potential signals to thechannels. At least one of the different pluralities of the electricalpotential signals are representative of potentials in the vicinity ofthe heart. The improvement further comprises means responsive to thechanging means for automatically reducing the amplitudes of the signalsrepresentative of potentials in the vicinity of the heart.

In accordance with a specific aspect of the present invention, thechanging means comprises selectively operable logic circuitry forinitiating the reducing means when signals representative of electricalpotentials in the vicinity of the heart are applied to each one of theplurality of electrocardiograph channels.

The invention thus provides an electrocardiograph wherein all non-chestsignals can be processed and displayed with a predetermined gain, andwherein the chest signals are automatically attentuated to precludeoff-scale excursions of the displaying device.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a, lb and 10 when connected asshown in FIG. 8 provide a diagrammatic representation of a multi-channelelectrocardiograph circuit;

FIGS. 2a and 212 when connected as shown in FIG. 9 provide a schematicrepresentation of a portion of FIG. 10 showing multi-channel amplifiercircuitry having amplitude reducing means;

FIG. 3 is a logic block diagram for actuating the components of FIGS.1a, lb, 10, 2a and 2b;

FIG. 4 shows a multi-trace electrocardiogram;

FIGS. 5 7 show modifications of FIGS. 2a and 2b as alternativeembodiments of the invention;

FIG. 8 is a block diagram showing the orientation of FIGS. la, 1b and1c,- and FIG. 9 is a block diagram showing the orientation of FIGS. 2aand 2b.

DESCRIPTION OF SPECIFIC EMBODIMENTS With reference to FIGS. 1a to 1c, aright arm (RA) electrical potential signal is applied through an RFfilter 10 to a buffer amplifier 12. The output of the buffer amplifier12 is applied to a terminal 16 of a Wilson Network 17 by a lead 14, andto a solid state switch 20 by a lead 18. The output of the bufferamplifier 12 is also applied to another solid state switch 24 by a lead22.

Similarly, a left arm (LA) potential signal and a left leg (LL)potential signal are applied through respective RF filters 26, 28 tobuffer amplifiers 30, 32. The LA output signal from the buffer amplifier30 is applied by a line 34 to another terminal 36 of the Wilson Network17, and by leads 38, 40 to a solid state switch 42. The output of thebuffer amplifier 30 is also passed by a lead 44 to another solid stateswitch 46.

In like manner, the LL output signal of the buffer amplifier 32 isapplied by a lead 48 to a third terminal 50 of the Wilson Network 17,and by a lead 52 to another solid state switch 54.

Each one of the solid state switches 20, 24, 42, 46, 54, thus fardescribed are elements of a ganged network of switches 62 which areactuatable to a conductive state upon application of a signal to a lead64. Upon actuation of the network 62 to a conductive state, LA and RAsignals pass through solid state switches 46 and 20, respectively, toleads 66, 67, re-

spectively, defining the input to Channel 1 of the electrocardiograph.Simultaneously, the LL and RA signals passed by the conductive solidstate switches 54, 24 re spectively, are applied to leads 68, 69,respectively, defining in input of Channel 2. Also, simultaneously, theLL and LA signals applied to the solid state switches 60, 42,respectively, are applied to Channel 3 input leads 70, 71, respectively.The arm and leg signals in Channels, 1, 2 and 3 are simultaneouslyapplied to differential amplifiers 72, 74, 76, respectively. The outputof the Channel 1 differential amplifier 72 is a difference signalbetween the LA and RA signals applied thereto which is commonly known asa lead 1 signal. The output of the Channel 2 differential amplifier 74is known as a lead 2 signal and is indicative of the difference betweenthe left leg and right arm signals applied thereto. Channel 3differential amplifier 76 generates an output signal known as a lead 3signal which is the difference between left leg and left arm signalsapplied thereto. The lead 1, 2 and 3 outputs from the differentialamplifiers 72, 74, 76 are applied to modulators 78, 80, 82 which act toisolate the patient from a subsequent amplifier circuit and from thechassis of the electrocardiograph. The lead 1, 2 and 3 outputs from themodulators 78, 80, 82 are respectively applied through DC blockingcapacitors 84, 86, 88 to adjustable gain amplifiers 90, 92, 94. Theoutputs from the adjustable gain amplifiers 90, 92, 94 are applied topower amplifiers 96, 98, 100 which in turn provide sufficient drive torespective galvanometers to move respective writing styluses 108, I10,112. The styluses 108, 110, 112, in turn, simultaneously generatesgraphic displays of the lead 1, 2 and 3 signals on a moving strip chartsuch as shown in FIG. 4.

At the end of a predetermined period of time, the actuating signal online 64 is removed therefrom to cause the ganged switches 62 to open.Simultaneously, an actuating signal is applied to a lead 113 which actsto close another ganged network of switches 114. The lead 22 alsoapplies a RA signal to a solid state switch 115 in the network 114. Alead 116 applies a signal representative of the average of the LA and LLsignals from the Wilson Network 17 to a solid state switch 117 and thenetwork 114. Similarly, a lead 118 applies a LA signal to a solid stateswitch 119, and a lead 120 applies a signal representative of theaverage of the RA and LL signals from the Wilson Network 17 to a solidstate switch 121 in a network 114. In like manner, a lead 112 applies aLL signal to a solid state switch 123, and a lead 124 applies a signalrepresentative of the average of the RA and LL signals from the Network17 to a solid state switch 125 in the network 114.

When the network 114 is in a conductive state as a result of a signalbeing applied to the lead 113, the solid state switches 115 and 117 passthe RA signal, and the LA and LL average signal, respectively, alongChannel 1 leads 66, 67 to the differential amplifier 72. Thedifferential amplifier 72 generates at its output a signal (AVR)indicative of the difference between RA signal, and the LA and LLaverage signal applied thereto. Simultaneously, the solid state switches119, 121 pass the LA signal, and the RA and LL average signal,respectively, to the Channel 2 leads 68, 69 for application to thedifferential amplifier 74. The differential amplifier 74 generates asignal (AVL) indicative of the difference between the LA signal, and theRA and LL average signal applied thereto. Solid state switches 123, 125

also simultaneously pass the LL signal, and the RA and LA averagesignal, respectively, to the Channel 3 leads 70, 71 for application tothe differential amplifier 76. The differential amplifier 76 generatesat its output a signal (AVF) representative of the difference betweenthe LL signal, and the RA and LA average signal applied thereto. TheAVR, AVL and AVF signals are further processed in the same manner asthat described hereinabove with respect to the leads 1, 2 and 3 signalsfor simultaneous display on a strip chart such as shown in FIG. 4.

Chest signals V1 through V6 are generated at points extending from thefourth intercostal space at the right sternal margin in a standardpattern across chest to the left midaxillary line at a horizontal levelwith the fifth intercostal space at the left medclavicular line. TheVl-V6 chest signals are applied through respective RF filters -135 torespective buffer amplifirs 136-141.

V1, V2 and V3 signals from the buffer amplifiers 136, 137, 138 areapplied by leads 142, 143, 144 to solid state switches 146, 147, 148 ina ganged switch network 145. A signal representing the average of theRA, LA and LL signals is applied by a lead 152 from the Wilson Network17 to each one of the remaining solid state switches 149, 150, 151 inthe network 145.

In like manner, leads 153, 154, 155 apply the V4, V5 and V6 outputsignals from the buffer amplifiers 139, 140, 141 to respective ones ofsolid state switches 156, I57, 158 in a still another ganged switchnetwork 159. The lead 152 also applies the signal representative of theaverage of the LL, RA and LA signals from the Wilson Network 17 to theremaining solid state switches 160, 161, 162 in the network 159.

After the ganged network 114 is opened by removing the signal from thelead 113, a signal is applied to a lead 163 for simultaneously changingeach of the switches 146-151 in the network to a conductive state.Closure of the switch network 145 applies the V1 signal and the averagesignal from switches 146, 149 respectively to leads 66, 67 of Channel 1for application to the input side of the differential amplifier 72.Simultaneously, switches 147, pass the V2 and average signals to leads68, 69 of Channel 2 at the input side of the differential amplifier 74.Also simultaneously, the switchs 148, 151 apply the V3 and averagesignals to leads 70, 71 of Channel 3, and to the differential amplifier76. The differential amplifiers 72, 74, 76 substract the average signalsapplied thereto from the respective V signals to generate at theirrespective outputs signals known as V1, V2 and V3. The V1, V2 and V3signals are processed through the remainder of the circuit forsimultaneous display such as shown as in FIG. 4.

After a predetermined period of time, the signal is removed from thelead 163 to cause the switches in the ganged network 145 to open, and asignal is applied to lead 164 to close the network 159. Closure ofswitches 156, pass the V4 signal and the average signal to differentialamplifier 72 in Channel 1. Simultaneously, the V5 signal and the averagesignal are passed by switches 157 and 161 to the input side of thedifferential amplifier 74 in Channel 2. Also, simultaneously, the inputside of the differential amplifiers 76 in Channel 3 received the V6signal and the average signal from switches 158, 162. The differentialamplifiers 72, 74, 76 respectively generate at their output sidessignals commonly known as V4, V5, and V6 signals. These sig nals areprocessed through the remainder of the circuit for display such as shownin FIG. 4.

The circuit of FIGS. 1a to also includes a defibrillation protectionnetwork. When defibrillation occurs, the input voltages applied to theRF filters 10, 26, 28, 130-135 tends to rise to approximately 3,000volts. To protect the electrocardiograph in the event of defibrillation,neon lamps 165-173 are parallelly connected to the Rf filters as shown.A suitable neon lamp is one that will fire at 125 volts, ionized atapproximately 80 volts. During normal electrocardiograph recording, theneon lamps 165-173 are effectively open circuits. However, if the inputvoltages rise such as during patient defibrillation, the neon lamps165-173 first fire, then ionize, to effectively short circuit the highpotentials through a lead 174 connected to the right leg of the patientand thereby protect the sensitive electrocardiograph circuits.

The circuit of FIGS. 1a to 10 also provides circuitry for reducinginterference caused by common mode voltages. The RA, LA and LL outputsignals from the buffers 12, 30, 32 are applied to respective leads 175,176, 177 for generating a summed signal on a lead 178. The lead 178applies the summed signal to a RI. driver circuit 179. The RL drivercircuit includes a l80phase inverting amplifier 13 and an emitterfollower 15 used as a buffer driver which applies an amplified summedsignal l80 out of phase with the patient common mode signals to the lead174 connected to the patients right leg. The out of phase signal appliedto the patients right leg tends to cancel out the common mode voltageeffects on the input signals applied to the RF filters 10, 26, 28,130-135.

FIGS. 2a and 2b shows a detailed schematic of the modulator circuits 78,80, 82 and of the gain controlled amplifiers 90, 02, 94. As describedabove, the outputs of the differential amplifiers 72, 74, 76 are appliedto respective modulator circuits 78, 80, 82. Since the components ineach channel of FlGs. 2a and 2b contain substantially identicalcomponents and operate in a like manner, only Channel 1 will bedescribed. However, it should be understood that Channel 2 and Channel 3simultaneously processes signals in the same manner as described withreference to Channel 1.

The output from the differential amplifier 72 is applied to atransformer 170 in the modulator circuit 78. A high frequency (e.g.100,000 Hertz) oscillator 170 drives the base of a transistor 171 tomodulate the signal applied to the transformer 170. The output from thetransformer 170 is demodulated by an amplitude detector diode 171. Theoutput from the diode 171 is filtered by RC components 172 and theoutput from the RC components 172 is applied to the DC blockingcapacitor 84 which forms part of a pulse shaping circuit 173. The pulseshaping circuit 173 provides an RC coupling to an input terminal 174 ofa negative feedback amplifier 175. The RC coupling is modified by acapacitor 174' and a resistor 175 to flatten out the initial portion ofthe RC decay. The gain of the amplifier 175 is controlled by a resistorfeedback network 176. The resistor feedback network 176 has selectivelyoperable panel switches 181-184 which act to selectively apply signalsdeveloped between serially connected resistors 186, 177-170, 179' to afeedback lead 177'. The switches 181-184 are each ganged withcorresponding switches in Channels 2 and 3, and are selectively operableto provide a quarter, a half, unity or double gain control to theamplifier 175. Operation of the quarter switch 181 acts to remove areset signal l2V from lead 214 which is connected to reset lead 214, andto permit passage of a signal developed between resistors 177 and 186 toa lead 187 and through the switches 182, 183, 184 in the positions shownto the feedback lead 177. Since the amplifier is a negative feedbackamplifier the greater the feedback signal the less the output signalgenerated on a lead 202' connected to a lead 188 for application to thepower amplifier 96. Operation of the switch 182 acts to maintain theother switches 181, 183 and 184 in the position shown and to pass alower amplitude signal developed between resistors 177 and 178 to lead189 through the switch 182, in the position not shown, a lead 190, andthe switches 183 and 184 in the positions shown to the lead 177. Sincethe feedback signal is now less than the feedback signal when the switch181 was depressed, the amplitude of the signal on the lead 188 will belarger. Operation of the switches 183 or 184 will further decrease thefeedback signal on the lead 177 to thus further increase the amplitudeof the signal applied to the power amplifier 96 by the lead 188.

In accordance with the present invention, the resistor feedback network176 also includes a panel switch 200 which when actuated to the positionnot shown acts to attenuate the signal applied to the lead 188 by theamplifier 175 whenever the V1, V2 and V3 or V4, V5 and V6 signals arebeing processed. When the switch 200 is in the position shown, anegative signal is applied by a lead 201 and a lead 205 to ganged solidstate switches 202, 203, 204 in the three channels. The negative signalapplied to the solid state switches 202, 203, 204 insures that theseswitches are maintained in a nonconducting state. When the panel switch200 is moved to the position not shown, a positive signal is applied bythe lead 201 to the logic circuit of FIG. 3 which when either one of theV1-V3 or V4-V6 signals are being processed causes the solid stateswitches 202, 203 and 204 to be changed to a conductive state.

As noted above, each one of Channels 1, 2 and 3 function in the samemanner. Accordingly, only the operation of Channel 1 will be describedwith the understanding that Channels 2 and 3 will both simultaneuoslyfunction in the same manner. When switch 202 is actuated to a conductivestate, resistors 206 and 207 are.

placed in parallel with the resistors 185, 186 in the feedback networkto increase feedback signal applied by the lead 177 to the amplifier 175irrespective of which one of the gain switches 181-184 are in anactuated state. Thus, the specific embodiment provides for selectivelyoperable means for automatically reducing or attenuating the V1-V3 orV4-V6 signals to preclude off-scale excursions by the styluses 108, 110,112.

In one embodiment, values of the resistors 206 and 207 are chosen todouble the signals developed between resistors 186, 177, 178, 179 and179, and thus halve the signals applied to the styluses 108, 110, 112.Suitable resistor values for the feedback circuit of this embodiment areshown in FIGS. 2a and 2b.

It will be noted that the output side of each one of the DC blockingcapacitors 84, 86, 88 are connected to a solid state switch 210, 211,212. Whenever a new set of body potential signals are applied toChannels 1, 2 and 3 a reset signal is applied to a lead 214 to changethe solid state switches 210, 211, 212 to a conductive state. When thesolid state switches 210, 211, 212 are in a conductive state, the DCblocking capacitors 84, 86, 88 are discharged to ground. The dischargefunction is carried out for a relatively short period of time such as0.5 seconds after which the reset signal is removed from the lead 214 tochange the solid state switches 210, 211, 212 to a non-conductive state.

It should also be noted that each one of the amplifier networks 90, 92,94 has a reset balance resistor network 220 for insuring that thevoltage at the input to the amplifier 175 is zero whenever a bodypotential signal is not applied thereto. Similarly, each one of theamplifiers has a gain balance resistor network 221 for insuring that theoutput of the amplifier 175 is zero whenever a body potential signal isnot being processed by the amplifier.

FIG. 3 shows a logic block diagram wherein a shift register 300 isentered by a pulse generated by actuation of an automatic start button(not shown) on the panel of the electrocardiograph, and the shiftregister 300 applies an actuating pulse to the lead 64 (FIG. 1b) toactuate the ganged switch network 62 to a conductive state such that thesignals applied thereto are fed to Channels 1, 2 and 3 to generate theleads 1, 2 and 3 signals for display such as shown in FIG. 4. After apredetermined period of time, the signal is removed from the lead 64 anda signal is applied to the lead 1 13 (FIG. lb) for actuation of theganged switch network 114 to pass the signals applied thereto to thethree channels for generation of the AVR, AVL and AVF signals fordisplay such as shown in FIG. 4.

After another predetermined period of time, the shift register removesthe signal from the lead 113 and applies a signal to the lead 163 (FIG.1b) to change the ganged solid state switch network 145 to a conductivestate. The ganged network 145 in a conductive state passes the V 1, V2,and V3 and average signals to Channels l, 2 and 3 for display of V1, V2,V3 values such as shown in FIG. 4. Simultaneously with the applicationof a signal to the lead 163, a signal is also applied to a lead 307 andto one input of an OR gate 308. The output side of the OR gate 308 isconnected to a small value short circuit protector resistor 308'. If thesignal on the lead 201 is negative (e.g.,-12V), the ganged switches 202,203, 204 (FIG. 2b) remain in a nonconductive state, and the V1-V3signals are recorded at the gain determined by whichever one of thepanel switches 181-184 are actuated.

However, when the panel switch 200 is actuated the negative voltage(e.g.,-42V) is applied to a resistor 200' now connected to the lead 201.When the OR gate 308 has a signal thereto, it generates a positiveoutput signal (e.g., +l2V) and a positive signal is applied via the lead205 to the solid state switches 202, 203, 204. The solid state switches202, 203, 204 are thus placed in a conductive state to insert theresistors 206, 207 in each one ofthe channels into parallel arrangementwith the resistors 185, 186 in the feedback network to thus reduce orattenuate the V1, V2 and V3 signals applied to the amplifiers 96, 98,100.

After another predetermined period of time the shift register 300removes the signal from the lead 163 and applies a signal to the lead164 FIG. lb) to actuate the ganged switch network 159 to a conductivestate, and thus apply the V4, V5, V6 and average signals to Channels l,2 and 3. As described in the preceeding two paragraphs, if the panelswitch 200 is in the position shown, the V4-V6 signals are recorded at again determined by the panel switches 181-184. However, if the panelswitch 200 is actuated to the position not shown, the V4-V6 recordedamplitudes are reduced by placing the resistors 206 and 207 intoparallel arrangement with the resistors and 186 in the feedback network.

After another predetermined period of time, the signal is removed fromleads 164 and 301, and a signal is applied to a standardization modecircuit (STD) for self-calibration of the electrocardiograph.

FIG. 3 also depicts starting a clock by actuation of an automatic startbutton (not shown). The clock determines the predetermined time periodsfor applications of signals to the leads 64, 113, 163, 307, 164 and 301and to STD. The clock also applies positive signals to the reset lead214 (FIG. 2a) to discharge the capacitors 84, 86 and 88 prior toapplication of new signals to Channels 1, 2 and 3 as describedhereinabove.

At the end of STD the register 300 applies a signal to HOLD of the clockand also to OFF of a chart drive. The register 300 also has a MANUAL SETmade for stopping the clock and maintaining a signal on anyone of theleads 64, 113, 163 and 164, or STD.

FIG. 5 shows an alternative circuit for reducing the gain of the signalsrepresentative of body potentials in the vicinity of the heart. In thiscircuit, a normally closed solid state switch 502 is substituted for thesolid state switch 202 of FIG. 2b, and an inverting amplifier 505 ispositioned in the lead 201. The resistors 206 and 207 of FIG. 2b arealso removed from the circuit. In this embodiment, when the panel switch200 is in the position shown in FIG. 2b, a negative signal (e.g., -l2V.)is applied to the inverting amplifier 505 which inverts the signal to apositive signal for application to the solid state switch 502 tomaintain it in a conducting state. When the solid state switch 502 is ina conducting state, a resistor 503 is placed in circuit with theresistor 504 to thus apply a relatively high signal to the input 174 ofthe negative feedback amplifier 175. However, when the panel switch 200is moved to the position not shown in FIG. 2b, the resistor 200' isplaced in the circuit containing the lead 201, and upon application of apulse to the leads 307 and 301 of FIG. 3, a positive signal is appliedto the inverting amplifier 505, which in turn generates at its output anegative signal to change the solid state switch 502 to a non-conductivestate. When the switch 502 is changed to a non-conductive state, theresistor 503 is taken out of the circuit to thus decrease the amplitudeof the signal applied to the input 174 of the negative feedbackamplifier 175. In this mode, the signals representative of voltagepotentials in the vicinity of the heart are decreased to precludeoff-scale excursions of the styluses.

FIG. 6 shows yet another alternative embodiment. In this embodiment, anormally opened solid state switch 601 is connected to the lead 201 andto a resistor 602. The solid state switch 202 and the resistors 206 and207 of FIG. 1b are removed from the circuit. When the switch 200 is inthe position shown in FIG. 2b, the solid state switch 601 is in anon-conductive state to maintain the resistor 602 out of parallel withthe resistor in the feedback line 177'. However, when the switch 200 ismoved to the position not shown in FIG. 2b, the resistor 200 is placedin the circuit comprising the lead 201, and when the shift register 300(FIG. 3) applies a signal to the leads 307 and 301, a positive signal isapplied to the solid state switch 601 to change it to a conductivestate. When the switch 601 is in a conductive state, the resistor 602 isplaced in parallel with the resistor in the feedback line 177' to thusincrease the signal fed back to the input 174 of the negative feedbackamplifier 175. In this manner, the output signal applied to the lead 188is decreased to preclude off-scale excursions of the signalsrepresentative of chest potentials.

FIG. 7 shows still another alternative embodiment wherein the solidstate switch 202 and the resistors 207 and 206 of FIG. 2b are removedfrom the circuit, and a solid state switch 701 is interconnected betweenthe resistors 186 and 177 and to a resistor 702 connected to ground. Aninverting amplifier 703 is also connected to the diode of the solidstate switch 701 and to the logic lead 201. When the switch 200 of FIG.2b is in the position shown, the negative signal (e.g., -12V.) isapplied to the inverting amplifier 703 which generates at its output apositive signal for maintaining the solid state switch 701 is aconductive state. When the switch 701 is in a conductive state, theresistor 702 is effectively placed in parallel with the resistors 177179, 170, 179 to maintain the feedback signals generated on the lead177' at a relatively low amplitude. However, when the switch 200 of FIG.2b is moved to the position not shown, the resistor 200' is placed inthe logic feedback line 201, and when the logic circuit of FIG. 3applies a signal to either one of the leads 307 or 301, a positivesignal is applied to the inverting amplifier 703 which in turn applies anegative signal to the solid state switch 701. The resistor 702 is takenout of the circuit to cause the feedback signals applied to the feedbackline 177 to increase and thereby decrease the amplitudes of the chestsignals applied to the lead 188.

In each of the preceding embodiments, the gain controlled amplifiers 90,92 and 94 are negative feedback inverting amplifiers. However, it isobvious to one skilled in the art that the inputs to the amplifiers 90,92 and 94 can be reversed and the feedback line 177' maintained at the174 amplifier input such that the amplifiers operate in a negativefeedback non-inverting mode. When the amplifiers 90, 92 and 94 are in anegative feedback non-inverting mode, the feedback resistor networks ofFIGS. 3, 6 and 7 can be used in the manner described to control theoutputs applied to the amplifiers 96, 98 and 100.

In yet another embodiment, the solid state switches 202 204 and theresistors 206, 207 are removed from the FIG. 2b circuit, and any one ofmany well known attenuating circuits can be placed at the output leads188 to the amplifiers 96, 98 and 100. The attenuating circuits (notshown) can be readily actuatable in response to signals generated by therespective positions of the panel switch 200 and the logic of FIG. 3.

In each of the foregoing embodiments, the amplifiers 90, 92 and 94 canbe a LM301A manufactured by National Semiconductor, Inc., Santa Clara,Calif.

In yet another alternative embodiment, the channel 1 3 signals can beapplied to serially connected amplifiers which apply predeterminedamplitude signals to the styluses 108 112. However, when signalsrepresentative of voltage potentials in the vicinity of the heart arebeing processed, one or more amplifiers in the serially connectedamplifier circuit can be bypassed to thus reduce or attenuate thesignals applied to the styluses.

Although shift registers suitable for carrying out the functions of thelogic block diagram shown in FIG. 3 are wall known in the art, animproved shift register circuit suitable for carrying out the functionsof FIG. 3 is disclosed in U.S. patent application Ser. No. 281,075, nowU.S. Pat. No. 3,753,124 for Manual Set System For Shift Register byErnest F. J. Graetz. U.S. patent application Ser. No. 281,075 is beingfiled concurrently herewith (Aug. 16, 1972), and is incorporated hereinby reference.

It is obvious that the ECG signals processed by the foregoingembodiments can be recorded or applied to a telephone circuit fortransmission and display at a remote site.

What is claimed is:

1. In an electrocardiograph comprising a plurality of parallel signalprocessing channels, each one of said channels including means foramplifying signals, means for simultaneously applying a plurality ofsignals representative of different body electrical potentials includingelectrical potentials in the vicinity of the heart to said channels, andmeans for simultaneously recording signals processed by said channels,the combination comprising: 7

means for automatically changing said applying means to sequentiallyapply different pluralities of body electrical potential signals to saidchannels, at least one of said different pluralities of body electricalpotential signals being chest signals representative of electricalpotentials in the vicinity of the heart, and

means in each one of said channels responsive to said changing means forreducing the amplitudes of the chest signals.

2. The electrocardiograph of claim 1 wherein said changing meanscomprises a plurality of switch networks corresponding in number to saiddifferent pluralities of body electrical potential signals, and a shiftregister for sequentially actuating said switch networks.

3. The electrocardiograph of claim 2 wherein said changing means furthercomprises a logic circuit connected to said shift register for applyinga signal to said reducing means when one of the switch networks isactuated to pass chest signals to said channels.

4. The electrocardiograph of claim 1 wherein said changing meanscomprises a plurality of switch networks corresponding in number to saiddifferent pluralities of body electrical potential signals, means forsequentially actuating the switch networks, and means responsive to saidactuating means for generating an initiation signal to said reducingmeans when said chest signals are applied to said channels.

5. The electrocardiograph of claim 4 wherein said re ducing meanscomprises an amplifier circuit having an adjustable gain in each one ofthe channels, said amplifier circuits each including means responsive tosaid initiation signal for lowering the gain.

6. The electrocardiograph of claim 5 wherein each one of said amplifiercircuits includes an amplifier feedback circuit comprising a pluralityof serially connected resistors, and a plurality of manually operableswitches for connecting points between successive ones of the resistorsand a feedback amplifier input, whereby operation of one of the manuallyoperable switches adjusts the gain to a predetermined level.

7. The electrocardiograph of claim 6 wherein said reducing means furthercomprises resistor means placed 1 l 1 2 in circuit in response to saidinitiation signal for adjustconnected resistors. ing the signal at thefeedback input in a direction to re- The electrocardiograph of claim 4further duce the amplitude of chest signals. prising a manually operableswitch for enabling said mi- 8. The electrocardiograph of claim 7wherein said initiation signal places said resistor means in parallelwith at least the first resistor in said plurality of serially tiationsignal generating means.

1. In an electrocardiograph comprising a plurality of parallel signalprocessing channels, each one of said channels including means foramplifying signals, means for simultaneously applying a plurality ofsignals representative of different body electrical potentials includingelectrical potentials in the vicinity of the heart to said channels, andmeans for simultaneously recording signals processed by said channels,the combination comprising: means for automatically changing saidapplying means to sequentially apply different pluralities of bodyelectrical potential signals to said channels, at least one of saiddifferent pluralities of body electrical potential signals being chestsignals representative of electrical potentials in the vicinity of theheart, and means in each one of said channels responsive to saidchanging means for reducing the amplitudes of the chest signals.
 2. Theelectrocardiograph of claim 1 wherein said changing means comprises aplurality of switch networks corresponding in number to said differentpluralities of body electrical potential signals, and a shift registerfor sequentially actuating said switch networks.
 3. Theelectrocardiograph of claim 2 wherein said changing means furthercomprises a logic circuit connected to said shift register for applyinga signal to said reducing means when one of the switch networks isactuated to pass chest signals to said channels.
 4. Theelectrocardiograph of claim 1 wherein said changing means comprises aplurality of switch networks correspOnding in number to said differentpluralities of body electrical potential signals, means for sequentiallyactuating the switch networks, and means responsive to said actuatingmeans for generating an initiation signal to said reducing means whensaid chest signals are applied to said channels.
 5. Theelectrocardiograph of claim 4 wherein said reducing means comprises anamplifier circuit having an adjustable gain in each one of the channels,said amplifier circuits each including means responsive to saidinitiation signal for lowering the gain.
 6. The electrocardiograph ofclaim 5 wherein each one of said amplifier circuits includes anamplifier feedback circuit comprising a plurality of serially connectedresistors, and a plurality of manually operable switches for connectingpoints between successive ones of the resistors and a feedback amplifierinput, whereby operation of one of the manually operable switchesadjusts the gain to a predetermined level.
 7. The electrocardiograph ofclaim 6 wherein said reducing means further comprises resistor meansplaced in circuit in response to said initiation signal for adjustingthe signal at the feedback input in a direction to reduce the amplitudeof chest signals.
 8. The electrocardiograph of claim 7 wherein saidinitiation signal places said resistor means in parallel with at leastthe first resistor in said plurality of serially connected resistors. 9.The electrocardiograph of claim 4 further comprising a manually operableswitch for enabling said initiation signal generating means.